Fluid barriers for use under cryogenic conditions such as storage tanks and pipelines are intended to prevent the egress of the cryogenic fluid towards materials behind the barrier. Typically, conventional fluid barriers are based on special materials having similar properties such as nickel-steel or special fibre-reinforced composite materials. Examples of such special fibre-reinforced composite materials include those composed of thermosetting plastic matrix materials (such as epoxy and polyurethanes) reinforced by structural fibres such as graphite, glass, such as S2 glass and E glass, and Ultra High Molecular Weight polyethylene.
As an example, WO 2006/003192 A1 describes the use of a fluid barrier in a thermally insulated container for storing liquefied gas such as LNG (liquefied natural gas), liquefied nitrogen, oxygen or carbon dioxide and liquefied hydrogen. The fluid barrier as disclosed in WO 2006/003192 comprises a plastic material such as polyurethane or epoxy or a combination thereof. If desired, the fluid barrier may be reinforced by the incorporation of glass fibres.
Although the fluid barrier according to WO 2006/003192 A1 functions already satisfactorily, it has been found that the use of fluid barriers based on such composite materials may result in the introduction of high stresses that have to be accommodated by the overall construction. In some cases this may lead to mechanical failure of the fluid barrier and/or the overall construction.
EP 0 465 252 A1 describes a container or conduit for compressed and/or cryogenic gas comprising a gas impermeable synthetic polymer forming a gas barrier. Structural fibres can be embedded in the gas impermeable synthetic polymer to form a composite material. Typically, the composite material has a low strain and high modulus. When made using suitable structural fibres mentioned in the patent specification typically the composite materials will have Young's moduli of more than 50 GPa.
U.S. Pat. No. 6,962,672 describes a high pressure vessel particularly for a space engine. The internal skin of the pressure vessel may use a polyamide having a Young's modulus between 1 and 2 GPa. The tensile strain at break is not mentioned and, moreover, the internal skin is not a composite. Around the skin a reinforcing winding is wound, made from e.g. carbon fibre or aramide fibres sold under the name “Kevlar”. These materials in the reinforcing winding have a very high Young's modulus.
It is an object of the present invention to minimize the above problem.
It is a further object to provide an alternative material for use as a fluid barrier, under cryogenic conditions, such as below −30° C., below −100° C., or even below −150° C.
It is a further object of the present invention to provide improved containment systems such as containers, pipes, tanks, vessels, conduits and caverns for cryogenic fluids.